Self-report and behavioral measures of attitudes and persuasion processes have relied on the bivalent action disposition aroused by the attitude stimulus despite the potential for response distortion. When peripheral somatovisceral measures have been used to investigate communication and attitudes, investigators have traditionally sought to identify responses that were inherently linked to specific affective states. The multiple determinants of somatovisceral responses and the tenuous links between inherent physiological responses and specific affective states have placed strong limits on the usefulness of prior physiological assessments of attitudes. Rather than relying on response dispositions or peripheral physiological responses, the proposed research exploits a more robust relationship between the late positive component of the event-related brain potential (ERP) and categorization processes to study attitude phenomena. In this approach, a subject's attitude serves as the criterion along which stimuli were implicitly or explicitly categorized while ERP's are recorded. In preliminary research, we have found that the more negative (positive) the attitude stimulus embedded within a short sequence of very positive (negative) stimuli, the larger a late positive potential (LPP) amplitude over the centroparietal scalp region. This LPP has manifested even when overt or verbal responses have not accurately reflected a subject's attitude. Finally, the LPP amplitude appears to be larger over the right than left hemisphere when a subject's attitude serves as the criterion along which stimuli are categorized. The primary goal of the proposed research is to use ERP's to compare and contrast the evaluative processes underlying affect and social attitudes, e.g., by examining differences between low and high arousing hedonic stimuli, positive and negative evaluative processes, and individual differences. A second goal is to follow-up preliminary evidence from our laboratory suggesting that evaluative and nonevaluative processes produce different spatial distributions of the LPP recorded at the scalp. Together, the proposed studies complement others in this application by extending the Center's focus to include social attitudes.